A hard disk device (HDD) which is one of external memories of a computer utilizes a magnetic disk as its recording medium. The magnetic disk is composed of a circular disc of aluminum or glass, a magnetic film formed by painting a surface thereof with magnetic material and a protective coating formed on the magnetic film. The surface of the magnetic disk should be as flat as possible and its recording performance or magnetic performance should be as good as possible. The flatness of magnetic disk is tested by means of a glide tester and the recording performance is tested by means of a certifier.
FIG. 3 is a schematic flowchart of a conventional manufacturing and testing process of a magnetic disk. In the magnetic film forming step 1, a magnetic film and a protective coating are applied onto a surface of a disc of such as aluminum, followed by the glide step 2 in which a surface of the magnetic disk is polished to improve surface asperity thereof. Even after the glide step 2, there may be some residual asperity of the disk surface in the form of protrusions. Such protrusions are usually removed in the burnishing step 3 by rotating the magnetic disk while flying a burnishing head above the surface of the magnetic disk with a minute gap. The number of protrusions still existing on the magnetic disk surface even after the burnishing step 3 is detected by a glide test head in the glide testing step 4. When it is found in the glide testing step 4 that there are residual protrusions the number of which exceeds a predetermined number, the process is returned to the burnishing step 3. This is repeated until the number of residual protrusions becomes smaller than the predetermined number.
On the other hand, when the result in the glide testing step 4 is favorable, the magnetic disk is shifted to the certification testing step 5 in which the magnetic performance of the disk is tested by a certification testing head to certify the quality of the magnetic disk.
It has been known that minute particles of disk material may be scattered in the glide step 2 and contaminate environment. Therefore, it is conventional to separate a room in which the glide step 2 is performed from a room in which the burnishing step 3 and the glide testing step 4 are performed. The steps 3 and 4 are performed by means of a single testing device provided in the latter room. Further, the certification testing step 5 is performed in a still another room by means of a certifier since there is a possibility of scattering of particles in the burnishing step 3.
FIG. 4 shows a construction of a main portion of a glide tester which performs the burnishing step 3 as well as the glide testing step 4. Such glide tester is disclosed in Japanese Patent Application Laid-open No. Sho 63-175278. A magnetic disk 1 to be tested is mounted on a spindle 2 and rotated in a direction .theta.. A pair of head positioners or head carriage mechanisms 3A and 3B are provided. The head carriage mechanisms 3A and 3B have arms pointing a rotation center O of the magnetic disk 1 with an angle therebetween. In FIG. 4, the angle is 90 degree. A burnishing head BH and a glide testing head GH are supported by end portions of the arms of the head carriage mechanisms 3A and 3B, respectively, and moved radially inwardly toward the rotation center O along radial lines R1 and R2, while keeping minute gaps with respect to a surface of the magnetic disk 1. Thus, the burnishing step 3 and the glide testing step 4 can be done with using the single device. In this case, it is possible to cause the burnishing head BH and the glide testing head GH to trace an identical track Tr so that the steps 3 and 4 are performed successively. Since, therefore, a result of burnishing can be known immediately by the following glide test, through-put of test process can be improved.
The certification testing step 5 may take a relatively long time. In order to reduce the test time, it is usual to divide a whole area of the magnetic disk radially to an inner region and an outer region and to perform the certification tests of the inner and outer portions in parallel by means of two certification testing heads supported on end portions of the head carriage mechanisms.
FIG. 5 shows a main portion of such system which is disclosed in Japanese Patent Application Laid-open No. Sho 62-103581. In FIG. 5, a whole effective area of a magnetic disk 1 is divided radially by an imaginary circle C which is a center line of the whole area of thereof which can be used effectively as a magnetic recording medium to an inner region 1a and an outer region 1b and certification tests of these regions are performed in parallel simultaneously by certification testing heads CHa and CHb supported by head carriage mechanisms 4A and 4B which move within the regions 1a and 1b, respectively.
As to the formation of the magnetic film on the magnetic disk, it is a recent tendency to form it by sputtering or plating rather than painting. A magnetic film formed by sputtering or plating is generally high quality in term of flatness and, therefore, the glide step 2 may be omitted. Further, since an amount of particles to be scattered during the burnishing step 3 is very small, it becomes unnecessary to provide a separate room for the certification testing step 5.
In a magnetic disk tester of this type, the steps 3 to 5 can be done by a single device and the parallel certification test is possible. FIG. 6 shows schematically a device of this type which is available from ProQuip, Inc., Santa Clara, Calif.
In FIG. 6, assuming a cartesian coordinates having an original point on a rotation center O of a spindle 2, a pair of head carriage mechanisms 5A and 5B which are movable in directions parallel to X and Y axes, respectively, are provided. A Y shifting mechanism 6y and an X shifting mechanism 6x are mounted on the head carriage mechanisms 5A and 5B, respectively. A head fixing plate 61a is fixedly secured onto a moving table of the Y shifting mechanism 6y, on which a burnishing head BH and a certification testing head CHa are mounted with a distance Y1 therebetween. Similarly, a head fixing plate 61b is fixedly secured onto a moving table of the X shifting mechanism 6x, on which a glide testing head GH and a certification testing head CHb are mounted with a distance X1 therebetween.
In operation, the burnishing head BH of the Y shifting mechanism 6y and the glide testing head GH of the X shifting mechanism 6x are positioned on lines passing through the original point O and moved by the head carriage mechanisms 5A and 5B in X and Y directions, respectively, to perform the burnishing step 3 and the glide testing step 4 in sequence repeatedly. When a result of the glide testing step 4 becomes acceptable, the certification testing head CHa on the Y shifting mechanism 6y is moved by the Y shifting mechanism 6y in Y direction by a distance Y1 and the certification testing head CHb on the X shifting mechanism 6x is moved by the X shifting mechanism 6x in X direction by a distance X1, so that the burnishing head BH and the glide testing head GH are switched by the certification testing heads CHa and CHb, respectively. Under this condition, the respective heads CHa and CHb are positioned on lines passing through the original point O and are moved in X and Y directions by means of the head carriage mechanisms 5A and 5B, respectively. Thus, the certification tests for the respective regions 1a and 1b separated as shown in FIG. 5 are performed.
For high density recording magnetic disk, the number of tracks is large and recording density is high. Further, there is a tendency that the higher the recording density of the magnetic disk makes the lower the test efficiency. Therefore, there is a strong request of user who is using the magnetic disk tester to improve the test efficiency. In order to satisfy the above mentioned request, the above mentioned heads must be positioned precisely at high speed. However, this is very difficult.
That is, since, in the case of the tester shown in FIG. 6, moment of inertia of the respective head carriage mechanism are large, it is impossible to position the heads precisely when the head carriage mechanisms are moved fast. On the contrary, when the positioning is made precise, the moving speed of the head carriage mechanisms is restricted necessarily, causing the test efficiency to be lowered.
In the tester shown in FIG. 6, the Y shifting mechanism 6y is mounted on the head carriage mechanism 5A and the X shifting mechanism 6x is mounted on the head carriage mechanism 5B. As a result, the moving direction of the head carriage mechanism becomes perpendicular to the shifting direction of the head. When the positioning of the head is made orthogonal to the moving direction of the head carriage mechanism, there may be errors produced in positioning of the head when it is moved at high speed. In addition to this problem, the construction of the shifting mechanism becomes complicated.
Further, when, in order to improve the test efficiency, the effective region of the magnetic disk is divided to a plurality of annular regions and certification tests are performed for the respective annular regions, there may a case where centers of the respective tracks in the respective divided regions as references are deviated due to positioning error to be occurred when the magnetic disk is a high recording density magnetic disk. Further, there is a risk that the centers of tracks in one region are different from those of other regions. With this, the quality certification to be given by the certifier for a high recording density magnetic disk is degraded.